Hitherto, for example, in an auxiliary machine drive system of a vehicle engine or the like, an auto-tensioner has been employed in order to prevent a belt slip at the time when the tension of a belt is changed.
For example, an auto-tensioner described in Patent Document 1 has a stationary member, a rotatable member which is supported to be able to rotate relative to the stationary member, and a coil spring which biases the rotatable member to rotate relative to the stationary member. A pulley on which a belt is wound is mounted to the rotatable member. The stationary member and the rotatable member have outer cylindrical portions for accommodating the coil spring therein. Further, on the insides of the outer cylindrical portion of the stationary member and the outer cylindrical portion of the rotatable member, in addition to the coil spring, friction members are arranged for damping the oscillation of the rotatable member. The friction members are allowed to slide on the stationary member or the rotatable member when the rotatable member rotates.
During the use of the auto-tensioner, muddy water, engine oil, and the like stick to the outer surface of the stationary member or the rotatable member and infiltrate into the inside through the gap between the stationary member and the rotatable member. When the muddy water and the like infiltrate between the friction member made of a rubber or a synthetic resin and a sliding object (the stationary member or the rotatable member), wear of the friction member is accelerated, and a damping effect is reduced due to a reduction in braking force. Moreover, there was concern that the infiltrating muddy water and the like may have an adverse effect on the durability of members other than the friction members.
As the auto-tensioner which prevents the infiltration of muddy water and the like, for example, there is one disclosed in Patent Document 2. The auto-tensioner has a structure in which a lip is formed to extend outward from a part of the peripheral edge of an opening portion of a stationary member (tensioner cup) and an outer race portion of a rotatable member (tensioner arm) extends to cover the lip, thereby suppressing the infiltration of muddy water and the like. The lip is disposed so as to be on the upper side when the engine is mounted. In addition, between the inner peripheral surface of the opening portion of the stationary member and the outer peripheral surface of an inner race portion of the rotatable member, a friction member (damping band) is disposed over the entire periphery.